Basic DC Electricity

Boat Electrical SystemsTerry SparksCommander USN Retired

AgendaWhy learn Electricity?What is Electricity?What is DC?Overview of Boat DC systemsThe Breaker Panel

Battery Types20 Minute BreakCharging SystemsBattery LoadingSafetyDC ElectricityWhy learn Electricity?Install equipment without cost for serviceInstalling equipment without fires What size fuse do I need for equipment? Impact of new device on battery last? Battery size to sail to Catalina? Can I use an existing circuit breaker? Other questions can be answered with a little knowledge.

What is ElectricityElectricity is:Electrons being pushed through a conductive material such as wire or metal by a voltage source. The limiting of electron flow is as a result of the resistance , the opposition to current flow.The energy delivered or used by a device is called power.What is ElectricityTypical Electrical TermsVoltage in Volts (V, E)Current in Amps (A, I)Resistance in Ohms ()Power in Watts (P)What is DCDC stands for Direct CurrentDirect Current - current/electrons flows only in one direction through a wire and an electrical device.

DC electric energy is supplied by your battery(s)Devices used for charging batteries provide DCPFlow -->>>>>PSprayEnergyCommon point earth & atmosphereSprinkler isOpposition to flowWater- +Common pointBatteryHeater/Resistance(Opposition to Flow)Current -->>>>>VHeat is Energy/PowerElectricalSimple CalculationsCalculations- +Common pointBatteryHeater/Resistance(Opposition to Flow)Current -->>>>>VWork DoneHeat / Energy/PowerElectricalVoltage in Volts = Current X Resistance = I X RCurrent in Amps= Voltage/Resistance = V/RResistance in Ohms= Voltage/Current = V/IPower in Watts= Voltage X Current = V X IVoltage and Power CirclesRIVVIPExample 1For a 25Watt bulb, what is the smallest fuse we can install?

The 25 Watts is at the rated voltage of 12.6 Volts

So the current is P/V

25W/12.6V = 1.98 Amps (approximately 2 amp fuse)

VIPExample 2When we turn the battery charger on the 2 A fuse blows:With the charger on the voltage may go to 14.5V?R=V/I so for a 25W component at 12.6VFrom before we found it I ~ 2A RIVRIVSo then the resistance is V/I or

12.6V/2A = 6.3 ohms

At the new Voltage of 14.5 Volts:

14.5V/6.3 ohms = 2.3A

Yep! The fuse would blow so it needs to be at least a 2.5A.Your Turn!My new radio says it draws 2 A. What is the Power?What is the Resistance?RIVVIPBoat Electrical SystemOverview of Boat DC systems- +BatteryBoat Ground (Metal things)Battery Select SwitchTo 2nd batteryDC PanelVHFRadioNavigation LightsFMRadioFuseBatteryChargerToBoatGroundFuseOrFuses Required?All devices should have a fuse or circuit breaker on a 12 Volt power feed.Batteries and Battery chargers.Devices connected directly to a battery A fused must also be installed within seven inches of the battery connection.Charging can be through battery selector switch.Still needs fuse on output of charger.Charging to Battery directly requires 2 fuses.

The Breaker PanelFrequently two sections, DC and ACBreakers should be DC rated for current and voltageThe current/wire size to be connected to the breaker.A 20 amp breaker connected to at least #12 wireA 15 amp breaker connected to at least #14 wireLong runs of wire should have the next larger sizeItems connected to the wire should be less than the breakerUse Marine stranded/tinned wire only

Battery Types19Battery Types Typical on BoatsThree classes of BatteriesStarting Batteries need lots of current availableRecommend a 1000 MCA batteryLow cost unitsAlso hook to thrusters and anchor windless

Battery Types Typical on BoatsThree classes of Batteries (cont.)House BatteriesHigh Amp-hour ratingDesigned to draw smaller currents for long periodsNeeds to be capable of many charging cyclesDual PurposeGood for Power Boaters OK for House Current.OK for Starting CurrentsNot as good if planning a lot of anchoring.Battery Types Typical on BoatsStarting batteriesStarting batteries start engines, not for deep discharge use. Many thin plates = maximum surface area, and maximum current output. Repeated deep discharges will result in capacity loss and ultimately in premature failureA common Misconception: Starting batteries should be kept on float charge. Float will encourage corrosion on the electrodes Result in premature failure. Starting batteries should be kept open-circuit but charged at least once every two weeks to prevent sulfation.

Battery Types Typical on BoatsDeep cycle batteriesSpecially designed deep-cycle cells are much less susceptible to degradation due to cyclingRequired for applications where the batteries are regularly dischargedSuch as boat house batteriesBatteries have thicker plates Can deliver less peak current Can withstand frequent Discharging and Charging.

Battery Types Typical on BoatsMarine Dual Purpose batteriesAre something of a compromise between the two types Able to be discharged to a greater degree than starting batteriesBut discharged less than a deep cycle batteries.Battery Types Typical on BoatsLead AcidSimilar to the ones in most carsContains water and acidCan Leak if turned upside DownMore maintenance Requires water to be addedTerminals must be cleaned

Battery Types Typical on BoatsLead AcidVoltage per cell when charged is 2.1VSo 6 cells in a 12 Volt Battery is 12.6 Volts (when charged)Golf Cart Batteries have 3 Cells or 6.3 VoltsHigh Capacity batteries, great for House BatteriesMost Charging cycles of any battery

Battery Voltages to think About Open-circuit at full charged: 12.6 V to 12.8 V Open-circuit at full discharged: 11.8 V to 12.0 V

Time to chargeBattery is at power ~ 12.2V Open Circuit.

After full charge Terminal voltage will drop quickly to 13.2 V and then slowly to 12.6 V.

Battery Voltages to think About Equalization charging for flooded lead acids only15 V+ for no more than 2 hours once a month. (I do 30-45 minutes every month) When all cells have equal specific gravity done.Battery temperature must be monitored.Make sure water level still good when complete

Gassing (Hydrogen Gas) threshold: 14.4 V At 15V make sure ventilation is good

Battery Types Typical on BoatsGel CellThe acid is mixed with a silica fume creating a gel-like electrolyte. Eliminates the electrolyte evaporationCan be mounted in any positionRequires special setup on most chargersThe least forgiving of the battery types

Battery Types Typical on BoatsAGM (Absorbed Glass Mat)Electrolyte is absorbed into a mat of fine glass fibersCan be mounted in any positionSealed and glass mat protects plates from shorting out with vibrationMost forgiving of all batteries for both Charge and discharge.Clearly the best battery for boats, but also the most expensive20 Minute Break1918171615141312111098765432Time to get back to Class10Charging Your Battery

Charging SystemsTypesAlternator on the EngineShore Power or generator via a Battery chargerSolar CellsWind GeneratorWater Wheel

Charging Multiple BatteriesTwo engines one batteryTwo engines two banksOne engine two banks

One engine two or 3 banks(~0.7V drop on these devices)Charging LevelsTypeBulk / AbsorptionMax CurrentFloat*EqualizeGeneric Flooded14.43013.515-17.5Generic Gel14.22513.8N/AGeneric AGM14.33013.45N/A* Precise (0.05 V) float voltage is critical to longevity; too low sulfation is almost as bad as too high corrosion and electrolyte loss

Multi-Stage ChargingLongest Life on BatteriesMulti-Stage ChargerBulk Charge A constant high current to initially charge the batteryAbsorption Constant Voltage Charge to top off the batteryFloat Charge Keeps enough voltage on the battery such that loads requesting current end up coming from the charger instead of the battery. Keeps the battery fully charged.Solar/WindAlternatorMulti-Stage ChargingEqualize to get longest Life - Lead Acid BatteriesSelectable Equalizing Charge Used as maintenance feature about once a month to knock off the material built up on the plates Result in an un-balanced charge per cell.Will significantly extend the life of your Lead Acid Cells15 V+ for no more than 2 hours once a month. When all cells have equal specific gravity it is complete.

Hydrometer/Battery Tester

Alternator on the EngineFactory Alternators typically do not provide 3 or 4 charging stages Can reduce battery lifeAlternators with an external regulator control typically do provide 3 or 4 charging stages.Will Provide Maximum Battery LifeBattery UseBattery LoadingSailors worry about loading more than power boatersWhen we are under sail they are draining the battery. Conservation through the use of LEDS is like adding another power source. DC lights draw about 2 Amps Similar LEDs 0.2A2 Amp-hours vs. 0.2 amp-hours

(See Table next Slide)GroupDeviceAmpsNumber in UseUse Hours / Sub TotalAmphoursCommunications10.8VHF Cockpit Xmit6.000.00VHF Cockpit Receive0.3024.07.20VHF Nav Xmit5.400.00VHF Nav Receive0.700.00VHF Transfer Switch0.0324.00.72PA Amp0.240.00.00HF Xmit3.000.00HF Receive1.402.02.80Charge Portable0.500.20.10Navigation62.2Cockpit Breaker0.5024.012.00GPS1.2024.028.80Chart Plotter0.3924.09.36Radar Ximit3.004.012.00Radar Standby2.200.00Navigation Lighting17.9Running Lights2.248.017.92Mast Head Light2.240.00Anchor Light1.380.00Other Lights0.0Spreader Lights5.070.00Pumps5.6Fresh Water7.000.21.40Bilge8.300.54.15Galley0.0DC Refrigerator6.000.00.00General Lighting30.8Incadescent Spots1.8012.03.60Flourescent1.7044.027.20Miscelanious0.0Anchor Windlass80.000.00Inverter/ 500 W45.000.00.00.00Battery RequirementsDischarge to 66%381.75Charging200W Photo Panels16.002.012.0384.00Altenator60.001.01.060.00Balance of Power (+ is reserve - is lost for day)62.25

Battery LoadingWhen you anchor over night, it is important to have enough energy (Amp-hours) to:Provide cabin lightsAnchor light all night Start the engine the next morning.An Isolated battery used only for starting is a smart chooseWatch a DVD, maybe Captain RonBattery SwitchingBetter Battery switch designThe Battery one, Battery two, and both switches are the worst way to control battery connection possible.Putting the switch in both when a battery is low drains the good batteryWill equalize both batteries to a lesser chargeGo through off to other batteryCharging may remain an issueHaving the switch in both provides for no backup.Not a good solution for a sailboats or trollersMay work ok for power boatsStill a poor solution

Better Battery switch designA better solution is 3 single switches. One for House Battery On/OffOne for Engine starting On/Off One that cross connects the load to the other load circuit. West Marine has a replacement module to make it simple to convert

(See diagram next page)A better solution To energize the house supply engage S2 To start the Engine Engage S1If Starting Battery is Low!Disengage S1 Engage S3 with S2 Still engagedTo use the Starting Battery on the HouseDisengage S2Engage S3 with S1 Still engaged S1, S2, & S3 engaged equals the Both position on a traditional Battery Selector Switch. All three should not be engaged as with the Both position, the charged battery will discharge to the un-charged battery.

Operation** Banks of (2) 6 volt Golf cart batteries in series May provide the most charging cycles and hence longest life.Ships DC GroundTo StarterTo Metering and Charging devicesTo Metering and Charging devicesS1S2S3House 1-many12V Deep CycleBatteries**Number Based on AH required.Starting BatteryWith High Cranking Current

Ties Loads together not BatteriesBoth/BypassAvailable as Replacement for 1, 2, both Switch

BLUE SEA SYSTEMS Battery Switch/DC Circuit PanelWM Model #: 163233 Manuf. Part #: 8080

SafetySafetyTipsImportant to ensure boat does not burn!Smaller wires connected to the battery must be fusedVoltages out of Chargers must be fusedWorm wires means to much currentWarn wires can result in shorts

SafetyTipsCheap crimp connectors can result in poor and possibly arcing connections (Or Intermittent operation)Shrink tube over connectors or use connectors that shrinkUse Crimping toolIf you solder connectors, make sure the solder does not wick up into the wire.Connectors without insulator on endSolder at connection only

Apply Solder Here

SafetyMore TipsWhile 12V DC systems are to low a voltage to kill you, boats with 24V could.In rare cases when a persons is sweating and has a low resistance enough current to kill you could be generated with as little as 24 voltsBe Safe, turn off the power before working on itWhile 12 Volts may not kill you, with all the current available it could burn you wiring up if shorted,The Test to FollowKeep it Safe When BoatingUse Marine Grade Products Only